The nanoscience of butterfly wings

Butterflies are known for their beautifully coloured and patterned wings. These striking patterns are not merely fantastic appearances to be admired; each wing serves a dual purpose. The top section (seen when the wings are open wide) is usually vibrant and used in attracting mates. The bottom of a wing (seen when they are closed) is often a different colour pattern to be used, either deterring predators or allowing the animal to blend in. In both cases, we can see that butterflies make good use of their brightly coloured wings and so it is important that these variations in colours exist.  

A blue pansy butterfly.

But how do butterflies achieve their famous and varied colours? A recent study in Nature Communications from an international collaboration of researchers (from Imperial, the National University of Singapore, University of Trieste and Diamond Light Source) took a closer look into the nanoscale structures responsible for this natural wonder. They found that the pigments in a butterfly’s wing, not only absorb certain wavelengths of light, but also change the physical structures in the wing to affect how light is reflected to produce the colour we see.

If you zoom in on a butterfly’s wing, you will find thousands of tiny overlapping scales. Each scale can have a different structure and contain a pigment of its own. During wing development, these scales secrete a substance called a cuticle, which is a highly complex, multilayered nanoscale structure. The pigmentation of the scale and the specific structure of the cuticle are known to be linked. However, the interplay between how these pigments and structures interact to reflect and tune a scale’s colour has not been studied in detail.

A typical scale structure.

This gap in our understanding is in part due to a lack of modelling techniques able to combine both 3D densities and colour mapping. During the recent study, the international team used a technique called Ptychographic X-ray computed tomography (PXCT) at Diamond’s I13-1 beamline. This technique uses diffraction patterns collected at different overlapping positions at nanometre resolution, which is made possible by the highly coherent and intense X-ray beams at I13-1. Using these, researchers were able to produce a 3D density map alongside the colours produced from scales of two different butterfly species.

Importantly, from studying the cuticle structure it was found that during early development the cuticle splits into two distinct layers. The “lower lamina” becomes a flat, dense structure at the base, while the “upper lamina” becomes a complex structure of rods and ridges on top. Once pigments are introduced into these structures, they easily infiltrate through the gaps in the upper layer, whilst being barely able to interact with the dense base layer, instead simply lying top of it. Because the pigment can infiltrate the upper layer, it is likely able to alter the rod and ridge structure. Therefore, depending on the pigment interaction with this structure, the light reflection could produce a very different colour.

Balakrishnan, D., Prakash, A., Daurer, B.J. et al. Nanoscale cuticle mass density variations influenced by pigmentation in butterfly wing scales. Nat Commun 16, 7085 (2025).